Device for exposing a sample to electromagnetic radiation, for testing the aging of samples

ABSTRACT

The invention relates to a method and device for the exposure of samples to radiation to test their ageing, and more specifically to a device having a chamber ( 30 ) comprising:  
     a sample-holder cage ( 40 ) rotating about an axis (H-H), and  
     means ( 15 ) for placing at least one electromagnetic radiation lamp ( 10 ) in a fixed position and supplying said lamp, in the central part of the cage ( 40 )  
     The invention provides for an air circulation system with a swirling air flow about the axis (H-H) of the cage, the air flow having essentially components that are tangential and/or radial to the periphery of the cage, and essentially an axial component (H) in the central part of the cage,  
     Preferably, the cage ( 40 ) is mounted rotationally on an axially hollowed-out hub ( 50 ), the air flow ( 1 ) getting discharged in the axial hollow of the hub.  
     Preferably the cylindrical chamber ( 30 ) comprises air inlet louvers ( 31 ) positioned appreciably on the periphery of the cage ( 40 ) that are directed non-radially.  
     It is provided, according to the invention, that the device is designed to work with the axis (H-H) of the rotary cage ( 40 ) positioned in a horizontal direction.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to the field of devices andinstruments with electromagnetic radiation sources to test theaccelerated ageing of samples under the effect of light, as well asother atmospheric conditions such as temperature, humidity and waterprecipitation. The tests relate especially to the behavior of samplesmade of polymer materials which are essentially sensitive to ultravioletradiation.

[0003] 2. State of the Prior Art

[0004] The natural ageing of materials under sunlight is simulated, in aknown way, by exposing samples to a source of electromagnetic radiationwhose spectral distribution has to be carefully chosen in order toobtain accelerated ageing that can be correlated with the ageingobserved under natural conditions.

[0005] There are known devices comprising a fixed bank of low-pressurearc tube lights that give ultraviolet radiation. This bank of paralleltubes is positioned so that it faces the samples to be tested.

[0006] The drawback of the radiation from low-pressure arc tubes is thatthere is low emissivity and an ultraviolet spectrum that is verydifferent from the solar spectrum. This vitiates the tests.

[0007] Another drawback is that these devices cannot be used to obtainhomogeneous exposure of the samples, so much so that the test resultshave poor reproducibility.

[0008] There are known devices using xenon arc lamps whose value is thatthey have a spectrum very close to the solar spectrum when they areappropriately filtered.

[0009] With recent developments in the technique, it is now possible, inan equivalent way, to adopt filtered medium-pressure mercury vapor lampswhose spectrum is very rich in ultraviolet rays and show highequilibrium between the longer-wavelength U.V.A. type ultraviolet raysand the shorter-wavelength U.V.B. type ultraviolet rays. This enablesthe efficient reproduction of the ageing process caused by sunlight.

[0010] There are known instruments for carrying out ageing tests inwhich the samples are mounted on a vertical, cylindrical sample-holderrotating around vertically positioned tubular xenon arc lamps.

[0011] The rotation of the samples about the xenon lamps provides foreven exposure to radiation.

[0012] However, these lamps release much heat and it is necessary toplan for open-circuit or closed-circuit air circulation in order tomaintain the samples at a controlled temperature.

[0013] These instruments have the drawback of exposing the samples toheterogeneous temperatures.

[0014] Indeed, the ventilation circuit has an air suction zone above thecylindrical sample-holder that prompts a vertical air flow as in achimney stack. The air flow gets heated while moving vertically alongthe lamps and the samples, so that the samples positioned at the top ofthe sample-holder are necessarily at a temperature greater than that ofthe samples positioned at the bottom. Identical samples located atdifferent heights are therefore subjected to different temperatures.This again affects the reproducibility of the tests. In practice,certain users are forced to interrupt the tests to switch the positionsof the samples being tested, between the top and the bottom of thesample-holder.

[0015] Devices are also known with parallelepiped-shaped test chamberhaving mercury lamps positioned vertically at the four corners of thechamber, along a small, rotating sample-holding cylinder placed at thecenter of the chamber. The lamps and the external face of the samplesare cooled by ventilated air circulation with air inlets opened in theside walls of the chamber and an air outlet capping the entiresample-holding cylinder at the top of the chamber.

[0016] One drawback of this device is that it takes up far too muchspace in relation to the small surface area of the samples that can betested in it.

[0017] This device also has the drawback of showing major losses oflight energy, since more than 75 percent of the light is not sentdirectly to the sample-holder.

[0018] This device therefore has low efficiency when the depreciationcost of the equipment added to the energy expenditure is related to thesurface area of the samples being tested, and this adversely affects thecost of the tests.

[0019] There also exist instruments comprising a rectangular testchamber in which there is mounted a cylindrical sample-holder cagemounted rotationally on a solid driving shaft. A laminar air flowtravels along the samples, propagating vertically between apertures madein the axis of the generatrix lines of the cylinder at the floor and atthe ceiling of the chamber in order to isolate the samples from the flowof hot air coming from the lamp and to homogenize the testingtemperatures.

[0020] Despite the laminar air flow, this instrument still has thedrawback of exposing the samples to different temperatures, as thelaminar air flow gets further heated in contact with the samples exposedto strong light radiation. In practice, the samples placed at the top ofthe cage are thus exposed to a temperature several degrees higher thanthat of the samples placed at the bottom of the cage.

[0021] The patent EP-0 320 209 thus describes an atmospheric testcabinet or cubicle comprising a sample-holder rack rotating about axenon light tube positioned vertically. The samples are cooled by alaminar air flow that travels vertically along the internal walls of thesamples positioned along the straight flanks of the rack. For reasons ofeconomy, the air flow has a limited flow rate.

[0022] This test cubicle having a vertical laminar air flow and a lowflow rate has the drawback of not providing for the efficient cooling ofthe samples and of inducing temperature differences between the samplesplaced at the bottom and those placed at the top of the rack.

[0023] The U.S. Pat. No. 4,760,748 describes another instrument for thetesting of accelerated ageing also comprising a cylindricalsample-holder frame, mounted rotationally about the vertical axis, andlight tubes, with a rising laminar air flow cooling the internal face ofthe samples. The cylindrical frame has solid walls pierced with two rowsof apertures firstly in order to place the samples and secondly in orderto form suction holes for a secondary air flow.

[0024] In fact, for the cooling, the instrument comprises an aircirculation system with two air flows, with a rising main air columnthat flows up in the sample-holder cylinder, traveling along theinternal face of the samples, and a peripheral secondary air flow thatstrikes the external face of the samples. The secondary make-up air flowcomes from a source of cold air. The secondary air flow is created bythe suction effect prompted at the holes of the cylinder by the ascentof the main air column. The holes have a variable shuttering system todose out the peripheral secondary air flow in relation to the risingmain air flow.

[0025] The drawback of this device lies in the complexity andparticularly great space requirement of its dual-flow air circulationsystem.

[0026] Another drawback is that the testing space of the device and itscapacity in terms of numbers of samples is quite restricted when relatedto the huge space requirement of the cubicle with its air-removalinstrumentation at the top, the blower system and the rotational drivingsystem at the lower part, as well as the peripheral air circulationsystem and the lateral cold air source.

[0027] This dual-air-flow cooling system also has the drawback of givingrise to substantial temperature differences between the irradiatedinternal face and the cooled external face of the samples.

[0028] The German document DE-A-32 43 722 has made known a device, thatis quite different, for the testing of resistance to light and weathervagaries. This device comprises a large ventilated chamber in whichthere is positioned a horizontal assembly comprising a ring of lighttubes inserted between two horizontal, concentric air conduits and asample-holder drum mounted rotationally around horizontal conduits. Thetwo conduits are connected to a fan and communicate with each other aswell as with the outside of the chamber so that outside air is blowninto the first conduit, then returns and gets inserted into the spacebetween the first and second conduits to move along the light tubes incooling them while it returns to the exterior.

[0029] As for the samples positioned on the outer drum, they are cooledseparately by another vertical air flow that circulates in a circuitprovided with another fan and a cooling exchanger as well as, ifnecessary, heating means.

[0030] This device therefore has two air circulation systems coolingfirstly the samples and secondly the light tubes.

[0031] In this device, the light tubes as well as a sprinkler system arepositioned in conduits that separate them from the samples. This has thedrawback of adversely affecting especially the exposure of the samplesto light and the efficiency of the system.

[0032] The device further has the drawback wherein the vertical air flowthat crosses the sample-holder drum does not provide any efficaciouscooling to the samples.

[0033] It is an object of the present invention to make a device forexposure to radiation to test the ageing of samples, by which samplescan be subjected to uniform temperature and radiation, without theabove-mentioned drawbacks.

[0034] In particular, it is a goal of the invention to provide forefficient ventilation of the samples during tests made with the device.

[0035] Another goal of the invention is to obtain a device having areduced number of lamps and a smaller space requirement.

[0036] Another parallel goal of the invention is to obtain a device ofsimple design with high luminous efficiency in relation to the surfaceof the samples exposed so as to reduce the cost of the tests.

[0037] Finally, it is also goal of the invention to facilitate thehandling of the samples prior to the ageing tests.

SUMMARY OF THE INVENTION

[0038] Briefly, these goals are achieved according to the invention bymaking a device comprising a rotary sample-holder cage whose rotationalaxis is preferably positioned horizontally, so that the samples arecyclically located in the upper part, and then in the lower part of thechamber, thus making it possible to disregard inherent temperaturedifferences, more essentially in providing that the device has aswirling air flow around the axis of the cage.

[0039] In the present document, the term “swirling air flow” isunderstood to mean the flow of any mass of air driven firstly by amotion of rotation and convergence about an axis and, secondly, by atranslation motion directed substantially in this axis. A swirling airflow is characterized also by a gyratory, helical or spiral movement ofair about an axis with a speed that is inversely proportional to thedistance from the axis.

[0040] In the device according to the invention, the air flow enters theperiphery of the cage in arriving crosswise to the axis and havingessentially components that are tangential and/or radial to theperiphery of the cage, and then gets discharged at the center of thecage in parallel to the axis, in having essentially an axial componentin the central part of the cage, thus advantageously providing for asymmetry and evenness or regularity of the air flow.

[0041] The presence of a swirling air flow can easily be detected bymeans of a smoke generator which causes the appearance of a spiralwinding of smoke that may rotate several times on the periphery of thecage, thus advantageously optimizing calorific exchange at the samplesbefore getting speedily discharged in the axis of the sample-holdercage. The air flow can thus rotate about a depression in forming a sortof funnel or vortex.

[0042] The invention can be obtained with a device for the exposure ofsamples to radiation to test their ageing, the device having a chambercomprising:

[0043] a sample-holder cage rotating about an axis, and

[0044] means for placing at least one electromagnetic radiation lamp ina fixed position and supplying said lamp, in the central part of thecage,

[0045] with the particular feature wherein the device comprises an aircirculation system capable of generating a swirling air flow about theaxis of the cage, the system comprising fixed air passage aperturespositioned around the periphery of the rotary cage and an air passagehole positioned in the axis of the cage.

[0046] Preferably, the device comprises an air circulation system withair inlets at the periphery of the cage and an air removal system in theaxis of the cage.

[0047] Preferably, the air circulation system comprises fixed air inletapertures arranged evenly on the periphery of the cage and beingrotationally symmetrical about the axis, each aperture being oriented ina direction contained between the directions that are radial andtangential to the periphery of the cage, and an air removal conduitpositioned in the axial prolongation of the central part of the cage,the conduit being oriented in a direction parallel to the axis.

[0048] Preferably, the cage is mounted rotationally on an axiallyhollowed-out hub, the air flow getting discharged in the axial hollow ofthe hub.

[0049] Preferably, the air circulation system comprises air suctionmeans positioned in the prolongation of the hollow of the hub.

[0050] Preferably, the air circulation system is an open circuit system,advantageously enabling the direct suction of cool air from thelaboratory.

[0051] As an alternative, the air circulation system can work in aclosed circuit.

[0052] According to the preferred embodiment of the invention, thecylindrical chamber comprises air inlet louvers positioned appreciablyon the periphery of the cage. It is advantageously provided that theperipheral air inlet louvers of the chamber will be directednon-radially and that each peripheral air inlet louver will have adepth, an aperture and an angle of tilt with respect to the radialdirection such that the radiation of each lamp positioned in the centralpart of the cage will not cross the inlet hole and will not directlyescape from the chamber.

[0053] According to the preferred embodiment of the invention, the cagecomprises central elements and peripheral elements extending in theaxial direction and connected by radial elements, the central andperipheral elements extending in a single half space demarcated by theradial elements.

[0054] According to the preferred embodiment, the cage comprisescircular elements with different diameters enabling the samples to bepositioned at different angles of exposure.

[0055] According to an advantageous alternative, the central elements ofthe cage develop helically about the axis.

[0056] According to the preferred embodiment of the invention, the cageis linked to the hub by a disengageable driving mechanism enabling freerotation of the cage.

[0057] Advantageously, the mechanism comprises means of disengagement inrotation under the effect of a borderline axial torque between the cageand the hub.

[0058] Advantageously, the mechanism comprises means of disengagement ordisconnection in translation under the effect of a borderline axialforce between the cage and the hub.

[0059] According to one alternative embodiment, the device comprises awater tank positioned so as to bathe one part of the cage.

[0060] Finally, according to the invention, the device is designed towork with the axis of the rotary cage positioned in a horizontaldirection.

[0061] The invention also relates to a method to test the ageing ofsamples having the particular feature of implementing a device of thiskind for exposure to radiation.

[0062] Preferably, the method comprises steps consisting in:

[0063] placing the samples in a sample-holder cage (40) that rotatesabout a horizontal axis (H-H),

[0064] fixedly positioning and supplying at least one electromagneticradiation lamp (10) positioned on or about the axis (H-H) of horizontalrotation,

[0065] generating a swirling air flow about the horizontal rotation axis(H-H) the swirling air flow having, at the periphery of the cage, arotational motion whose component is included between the tangentialdirection and the radial direction, the swirling air flow having atranslation motion at the center of the cage, the component of which issubstantially parallel to the axial direction.

[0066] The invention can also be obtained with a method for the testingof the ageing of samples comprising the steps consisting in:

[0067] subjecting the samples to vertical rotation about one or moreelectromagnetic radiation lamps positioned on or about the horizontalrotation axis, and

[0068] generating a swirling air flow about the rotation axis of thesamples, the air flow essentially having components perpendicular to theaxis of rotation, at the samples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Other goals, features and advantages of the present inventionshall appear from the following description of an embodiment givenpurely by way of a non-restrictive example, the description integratingthe attended drawings of which:

[0070]FIG. 1A is a schematic view in axial section of the radiationexposure device according to the invention,

[0071]FIG. 1B is a schematic front view in cross-section of the deviceaccording to the invention,

[0072]FIGS. 2B, 2A and 2C are views of an embodiment of the deviceaccording to the invention, with retracted cap, FIG. 2A showing thedevice without cap and without lamp-bearer, seen in an axial section,FIG. 2B showing the retracted cap in a three-quarter view toward theinterior, FIG. 2C showing the kinematic chain of the device, seen in across-section toward the rear along the line C-C of FIG. 2A,

[0073]FIGS. 3A et 3B show a profile view and a cross-section view ofdetails of an advantageous embodiment of a cap for a device according tothe invention,

[0074]FIGS. 4A et 4B show an axial section and a front view of anadvantageous embodiment of a disengageable drive mechanism for asample-holder cage of a device according to the invention,

[0075]FIG. 5A shows a view in an axial half section and a half-profileof an advantageous embodiment of a disengageable drive mechanism for asample-holder cage of a device according to the invention, and

[0076]FIG. 5B shows a front and half cross-section view of thedisengageable drive mechanism of FIG. 5A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0077] In FIGS. 1 to 5, it can clearly be seen that the device is,preferably, generally circular and is rotationally symmetrical about anaxis H-H designed to be positioned advantageously in a horizontaldirection.

[0078] In the following description of the embodiment and the operation,it is considered, to simplify matters, that the device is rotationallysymmetrical about the axis H-H. Geometries of greater complexity may beenvisaged by those skilled in the art without departing from theframework of the invention.

[0079]FIG. 1A thus shows that the device according to the inventioncomprises a cylindrical and circular chamber 3, 30. Alternatively, thedevice may comprise a chamber that is cylindrical but with a sectionthat has a square, rectangular or other form. The chamber has aremovable cap 30, preferably shaped like a bowl, that gets hermeticallyfixed to a fixed deck 3. The cage 3, 30 contains a circularsample-holder cage 40 which can be made according to the example ofFIGS. 2 and 4, out of a frame of metal rods 41 to 47 arched into theform of circular elements 41,42,43,44,45,46 and curved elements 47 laidout in quarters and joined together.

[0080] The cage 40 is fixedly joined, by means of a circular drivingpiece 49 and a disengageable mechanism 55,56,57,58,59 with a hub 50-51.

[0081] The hub 50-51 is mounted rotationally, possibly on a rollerbearing or ball bearing 5, on the deck or decks 2-3 which offer a fixedsupport.

[0082] The hub 50 is rotationally driven by a kinematic chain comprisingan off-centered motor 20 connected by a gear or chain transmissionsystem 21, 22.

[0083] According to the preferred embodiment of the invention, the hub50-51 is completely hollowed out axially, the hollow forming an air flowremoval conduit.

[0084] Similarly, according to the preferred embodiment, the centralpart of the sample-holder cage 40 is hollowed out, and no rod of theframe appears in the central part of the cage which corresponds to theprolongation of the hollowed-out part of the hub 51.

[0085] Indeed, the invention provides for the fixed positioning of oneor more electromagnetic radiation lamps 10 in the central part of therotating cage 40.

[0086] The lamp or lamps 10 are connected, namely fixed and electricallypowered, directly by means of an axial part 15 having radial arms 16, 17in a star-shaped arrangement, to the fixed deck 2, or indirectly bymeans of the body 18 of a fan 1.

[0087] If only one ultraviolet lamp 10 is fitted into the deviceaccording to the invention, it is preferable that the lamp 10, which isgenerally tube-shaped or is rotationally symmetrical, should bepositioned in the central part of the cage, the axis of the lamp beingpositioned in the axis H-H of the cage.

[0088] If two or more lamps equip the device according to the invention,it is preferable that the lamps should be positioned symmetrically aboutthe axis of the cage and in parallel to the axis H-H.

[0089] In a particularly advantageous way, the arrangement of the lampor lamps 10 in the central part of the sample-holder 40 on or about therotation axis H-H, enables the samples to be exposed in rotation to aluminous flux that is perfectly homogeneous (provided that the samplesare positioned in parallel and at the same radial distance from theaxis).

[0090] It is also provided, according to the preferred embodiment of theinvention, that the device will comprise air suction means 1 positionedin the prolongation of the hollow of the hub 50.

[0091] It is provided, for example, that a fan 1 will be positioned inthe rear prolongation of the hollow of the hub 50.

[0092] The fan 1 may be affixed to the fixed rear deck 2.

[0093] Advantageously, the central parts of the cage 40 and of the hub50, as well as their extended portions are completely unencumbered,except for the lamp-holder 15, so as to allow the free passage of theair flow.

[0094] Thus, according to the invention, the air flow is discharged inthe axial direction H-H to the center of the cage 40, the deviceadvantageously comprising a cage 40 and a hub 50 whose central part iscompletely hollowed.

[0095] Furthermore, it is provided in the invention that air inlets31,32,33, . . . ,36,37,38 will be arranged on the periphery of the cage40.

[0096] According to the preferred embodiment of the invention, thecylindrical chamber 30 thus comprises louvers 31 to 38, namely airintake apertures, pierced in the cylindrical or near-cylindrical(slightly conical) rim of the cap 30 or more generally of the chamber.

[0097] During the tests it is planned to place the samples on theperiphery of the cage, in fixedly joining them to the circular elements41,42,43 of the frame of the cage, especially by means of clamps.

[0098] It is commonly considered that the samples are cut out intoplates or boards, generally plane-shaped, so much so that the samplesoccupy surfaces that are secant or tangential to the periphery of thecircular cage 40, as illustrated in FIG. 1B.

[0099] During operation, the samples are therefore in a position wherethey are tangential or secant to the periphery of the cage 40, the cageis put into rotation and the air suction means 1 start a flowcorresponding an air removal in the axis H-H of the cage 40, the lamp 10and the hub 50.

[0100] In a particularly advantageous way, the air heated by the lamp orlamps 10 in the axial position is discharged directly without heatingthe samples.

[0101] The convection heat released by the lamps during operationtherefore does not disturb the temperature of the samples duringtesting.

[0102] Furthermore, the air removal prompts an air inflow at theperiphery of the chamber 30. This air inflow strikes the samplesorthogonally or at an angle of incidence with respect to their plane, asillustrated in FIG. 1B.

[0103] Advantageously, the incidence of the air flow on the samplesimproves the thermal exchanges.

[0104] Contrary to the devices of the prior art, the samples thereforedo not have a laminar air flow traveling along them but are subjected toan incident, swirling air flow.

[0105] In certain embodiments, the air inflow may be strictly radial atthe level of the samples placed on the periphery of the cage 40.

[0106] This case arises especially when each air suction louver 31, 32,33, . . . is pierced radially in the cylindrical part of the chamber 30in assuming that the rotation of the cage 40 does not modify thecirculation of air.

[0107] In other embodiments, the air inflow at the periphery of thesample-holder cage 40 comprises both a radial component and a tangentialcomponent, so much so that the samples are subjected to an air flowhaving a certain angle of incidence.

[0108] In the preferred embodiment, it is thus planned to piercenon-radial louvers 31 to 38 on the periphery of the cylindrical chamber30.

[0109]FIGS. 3A and 3B thus show that the quasi-cylindrical rim of thecap 30 of the chamber is notched by fine apertures 31,32,33, . . .,36,37,38 forming axially plotted slots, these slots having theparticular feature of penetrating not in a radial plane but obliquely tothe radial direction; at the limit, the apertures 31 to 38 may be almosttangential to the cylinder of the cap 30.

[0110] In a particularly advantageous way, the oblique holes 31 to 38enable the air inflow to have tangential and radial components at thelevel of the samples placed on the periphery of the cage 40.

[0111] The circulation of air thus prompts a swirling air flow about theaxis H-H of the cage 40, the air flow having practically no axialcomponent but only components tangential and/or radial to the peripheryof the cage 40, while the air flow has only one axial component H-H atthe center of the cage 40.

[0112] In the present document, the expression “swirling air flow”covers the borderline case in which the air flow at the periphery of thecage has only a radial component as well as the other borderline case inwhich the air flow at the periphery of the cage has only a tangentialcomponent.

[0113] The circulation of air is thus advantageously similar to a siphonmotion about the axis of the cage, thus providing for optimum thermalexchanges at level of the samples.

[0114] Another essential advantage of the oblique positioning of the airinlet louvers 31 to 38 at the periphery of the cylindrical chamber 30 isthat it blocks the direct output of radiation from the lamp 10 whileenabling the passage of the air in a manner similar to that of thelouver arrangement in a blind or shutter.

[0115] In the preferred embodiment of the invention, each louver slot 31has a limited aperture but a sharp angle of tilt with respect to theradial direction as well as a great depth, so that the direct radiationfrom each lamp 10 positioned in the central part of the cage does notcross the louver 31 and does not escape from the chamber.

[0116] Furthermore, it is provided optionally, as shown in FIG. 2A, thatthe cap 30 will comprise a central port 39 made of anti-U.V. glass.

[0117] This port 39 whose glass cuts off the ultraviolet radiation, canbe advantageously used to observe the samples during testing, inpreventing harmful radiation from the lamp. Advantageously, the centralpart of the port 39 may be masked by a central part fixed by radial armsin a star-shaped arrangement (not shown).

[0118] The cap 30 is preferably made of sheet metal. It is made byswaging, which gives a slightly conical, near-cylindrical cap.

[0119] A light embodiment of this kind has the advantage of limiting thecost of the equipment and the investment for the ageing test.

[0120]FIGS. 4A and 4B show that the cage 40 is preferably made out ofsemi-rigid metal wires or rods 41 to 47.

[0121] The main advantage of such an embodiment is that it limits theweight of the cage 40, hence the size of the driving motor 20.

[0122] Such an embodiment also facilitates the circulation of air andthe handling of the samples.

[0123] This light embodiment also has the advantage of limiting the costof the equipment.

[0124] In first simplified embodiment, the cage 40 is formed by circularelements 41,42,43 of identical diameter, fixedly joined by radiatingelements 47 arc-shaped as in a basket or in a squirrel's wheel. Theradiating elements 47 simply comprise a portion parallel to the axis tofix the circular elements 41,42,43 and a radial portion to get fixed toa washer 49 of average diameter, fixedly joined to the driving hub 50.

[0125] In another embodiment, illustrated in FIGS. 1A and 2A, the cagehas several circular elements 41,42,43 and 44-44 having differentdiameters to be able to position plane samples, either perfectlyparallel to the axis by fixing them, for example, to the elements41,42,43 of the same diameter or obliquely to the axis in fixing themfor example to the elements 41 and 42 having different diameters.

[0126] Advantageously, this multiple-position frame provides for thepositioning of samples of different lengths at different angles ofradiation and at different distances from the light source, thusenabling the exposure of samples of different lengths to the sameintensity of illumination.

[0127] In the preferred embodiment, shown in FIG. 4, the cage 40 has aparticular umbrella-shaped frame.

[0128] The frame is formed by curved elements 47 positioned in quartersalong radial planes so as to radiate around the hollowed-out, centralpart of the cage 40.

[0129] As can be seen in FIG. 4A, each curved element 47 has one centralportion or element 47′ extending in parallel to the axis H-H to theboundary of the hollowed-out central part of the cage 40. The centralelement 47′ is connected to a portion or element 47″ extending in theradial direction heading opposite from the center. This radial element47″ is itself connected or prolonged by a peripheral element 47′″parallel to the axis, which demarcates the periphery of the cage 40.

[0130] The particular feature of the frame of the cage 40 of FIG. 4 isthat the central portion 47′ and the peripheral portion 47″′ of eachcurved element 47 are located in the same half-space demarcated by theplane of the radial portions 47″′. Each curved element 47 therefore hasa hook shape.

[0131] Subsequently, the circular elements 41,42,43,44 are fixed,especially by soldering, to the peripheral portions 47′″ of the curvedelements 47 to form the frame of the circular cage 40. Similarly, smallcircular elements 45 and 46 may be fixedly joined with the centralportions 47′ of the curved element 47 to complete the formation of theframe and advantageously increase the rigidity of the circular cage 40.

[0132] Finally, the central portions 47′ of the frame of the cage arefixed by fastening pieces, soldering or any other means to awasher-shaped part 49 designed to be fixedly joined to the hub 50.

[0133] An umbrella-shaped cage frame of this kind can advantageously beused to arrange instruments fixedly within the rotary cage (arrangementnot shown).

[0134] The instruments, which are sensor or actuator type instruments,are attached to the fixed-support deck 3 of the device and project outof the deck (in parallel or obliquely with respect to the axis) to getengaged within the rotary cage 40 without affecting the rotation.

[0135] In one example (not shown), it is provided advantageously that atemperature probe will be attached to the deck 3, above the axial lamp10, the active end of the probe moving forward between the lamp and thesamples without thereby preventing the rotation of the cage.

[0136] In another example (not shown), it is provided that awater-spraying bank will be positioned beneath and parallel to the axiallamp 10, in fixing it to the deck 3 to connect it to a water inlet.

[0137] Advantageously, the bank is thus immobilized within the rotarycage parallel to the plane of the samples, which are then evenly sprayedthroughout their surface at each rotation cycle.

[0138] Furthermore, according to an improved embodiment (which is notshown) it is provided that the central portions (47′) of the curvedelements that extend in the axial direction H-H are not rectilinear buthelically wound about the axis H-H of the cage 40.

[0139] The advantage of an improvement such as this is that it preventsa sample from being partially plunged into the shadow of the centralportion of a curved element. The electromagnetic radiation from thecentral lamp thus uniformly reaches each sample, whatever its positionon the periphery of the cage.

[0140] It is also provided, according to one advantageous option thatthe device according to the invention will comprise a water tank bathingthe lower portion of the rotary cage.

[0141] A half-moon shaped basin (not shown) may thus the fixed to thebottom of the deck 3 of the device, the cage 40 being partially plungedinto the water filling the basin.

[0142] A device of this kind can be used to test the behavior of thesamples in ageing under the combined effect of humidity, water immersionand electromagnetic radiation such as ultraviolet radiation;: thesefactors advantageously cover most of the natural agents of ageing.

[0143] Now, from the mechanical viewpoint, the cage 40 is rotationallydriven by a kinematic chain 50 comprising particular arrangements asillustrated in FIGS. 2A and 2C.

[0144] It is advantageously provided that the drive motor 20 will beoff-centered instead of being located in the axis H-H of the cage 40.

[0145] This enables the central hollowed-out central portion of thedevice and its prolongation to be completely unencumbered, so as not tohamper the circulation of air.

[0146] The motor 20 is fixed to a deck 2 with a fixed support. Theoutput pinion 21 of the motor drives a toothed ring 52 fixed to the hub50-51.

[0147] The transmission can be done either directly by gear mechanism,the pinion 21 and the toothed ring 52 being in contact, or indirectly bymeans of a chain or by a belt 22 tensioned between a pinion 21 and agrooved ring 52, as shown in FIG. 2C, or again by any other transmissionmeans.

[0148] In the exemplary embodiment of FIGS. 2A and 5A, the driving ringor plate 52 is attached by screws to a nut 53 stopped on the screwthread of the hub 51.

[0149] The nut 53 is also used to block a cylindrical spacer 54 againstthe ring of the ball bearing 5 or the circular rim of the deck 3.

[0150] Since the other end 55 of the hub is flared, the hub 51 is thenrotationally immobilized with respect to the fixed-support deck 3.

[0151] Finally, in a particularly advantageous way, it is provided thatthe cage 40 will be connected to the hub 51 by means of thedisengageable mechanism 50.

[0152] The hub 50 is thus constituted by two concentric bodies 57 and 51with flared ends 59 and 55, fitted into each other.

[0153] As illustrated in FIG. 5A, the body 57 of the hub 50 has a flaredfunnel shape that ends in a plane circular end 59, with hollowed-outscrew threads 58 to attach the cage 40 by means of a washer 49.

[0154] The other end, which is cylindrical, of the body 57 of the hub 50has a ring-shaped groove 56 hollowed in it throughout the rim.

[0155] Furthermore, the ring-shaped groove 56 has several hemisphericalcavities 56′ hollowed out in it at several points of its rim withoutdeepening the dip of the groove 56. According to the example of FIG. 5,it is thus planned to position three cavities 56′ at equidistance, at120° with respect to one another, on the rim of the ring-shaped groove56.

[0156] In a correlated way, the flared end of the main body 51 of thehub 50 has tubular housings 55, corresponding to the cavities 56′ fordeepening the groove 56 of the end body 57.

[0157] Each housing 55 is designed to receive a ball and a spring heldby pressure-setting screw.

[0158] When the end body 57 is fitted into the main body 51 of the hub50, each ball there gets engaged in the ring-shaped groove 56, and thengets blocked at the bottom of the corresponding hemispherical cavity56′.

[0159] Since the balls are kept at the bottom of the cavities 56′hollowed out in the groove 56, this mechanism blocks the body 57 intranslation and in rotation with respect to the body 51 of the hub, in amanner similar to what happens during the keying of a plug in a lockcylinder.

[0160] However, if excessive torque is exerted to the body 57 ascompared with the body 51 of the hub 50, the balls are pushed back outof their respective cavities 56′ and the body 57 starts rotating freelyabout the body 51, with the balls remaining engaged in the ring-shapedgroove 56.

[0161] This mechanism very advantageously enables a disengagement inrotation of the cage 40 with respect to the hub 50, when an excessiveaxial torque appears between the cage and the hub.

[0162] Advantageously, this disengageable mechanism enables an operatorto rotate the cage 40, while the motor 20 is at a halt.

[0163] Similarly, this mechanism prevents the motor 20 from beingaffected when the cage 40 gets accidentally locked in rotation.

[0164] Furthermore, this mechanism very advantageously enablesuncoupling in translation between the cage 40 and the hub 50 whenexcessive axial traction is exerted on the cage.

[0165] Indeed, by the exertion of traction force on the end body 57 inthe axial direction, frontward, the balls finally escape from the bed ofthe ring-shaped groove 56 and the end body 57 gets disconnected from themain body 51 of the hub 50.

[0166] This mechanism makes it possible to retract or disengage the cageof the device in translation.

[0167] Finally, it is advantageously provided that each housing 55 willcomprise one end reduced to a diameter smaller than that of the balls,to prevent the balls from escaping from the housings 55 when the body 57gets disconnected.

[0168] Other embodiments, alternatives and improvements can beimplemented by those skilled in the art without departing from theframework of the invention, the object of the protection being definedin the following claims.

1. Device for the exposure of samples to radiation to test their ageing,the device having a chamber comprising: a sample-holder cage (40)rotating about an axis (H-H), and means (15) for placing at least oneelectromagnetic radiation lamp (10) in a fixed position and supplyingsaid lamp, in the central part of the cage (40), characterized in thatthe device comprises an air circulation system capable of generating aswirling air flow about the axis (H-H) of the cage, the systemcomprising fixed air passage apertures (31, 32, 33) positioned aroundthe periphery (41) of the rotary cage (40) and an air passage hole (50)positioned in the axis (H-H) of the cage.
 2. Device according to claim1, characterized in that the air circulation system comprises fixed airinlet apertures (31-38) arranged evenly on the periphery (41) of thecage (40) and being rotationally symmetrical about the axis, eachaperture (31, 32, 33, . . . , 38) being oriented in a directioncontained between the directions that are radial and tangential to theperiphery of the cage, and an air removal conduit (50) positioned in theaxial prolongation (H) of the central part of the cage (40), the conduit(50) being oriented in a direction parallel to the axis (H-H).
 3. Deviceaccording to claim 1 or 2, characterized in that the cage (40) ismounted rotationally on an axially (H-H) hollowed-out hub (50), the airflow getting discharged in the axial hollow of the hub.
 4. Deviceaccording to claim 3, characterized in that air circulation systemcomprises air suction means (1) positioned in the prolongation of thehollow of the hub.
 5. Device according to one of the claims 1 to 4,characterized in that the air circulation system is an open circuitsystem.
 6. Device according to one of the claims 1 to 5, characterizedin that the cylindrical chamber (30) comprises air inlet louvers (31-38)positioned appreciably on the periphery of the cage (40).
 7. Deviceaccording to claim 6, characterized in that the peripheral air inletslouvers (31-38) of the chamber (30) are directed non-radially.
 8. Deviceaccording to claim 7, characterized in that each peripheral air inletlouver (31) has a depth, an aperture and an angle of tilt with respectto the radial direction such that the radiation of each lamp (10)positioned in the central part of the cage (40) does not cross thelouver (31) and does not directly escape from the chamber (30). 9.Device according to one of the claims 1 to 8, comprising means (15) toaxially position an electronic radiation lamp (10) on the axis (H-H) ofthe cage.
 10. Device according to one of the claims 1 to 9, comprisingmeans to symmetrically position electromagnetic lamps about the axis ofthe cage.
 11. Device according to one of the claims 1 to 10,characterized in that the cage (40) comprises central elements (47′) andperipheral elements (47″′) extending in the axial direction (H-H) andconnected by radial elements (47″), the central and peripheral elements(47′,47″′) extending in a single half space demarcated by the radialelements (47″).
 12. Device according to one of the claims 1 to 11,characterized in that the cage comprises circular elements (41, 44, 44′)with different diameters enabling the samples to be positioned atdifferent angles of exposure.
 13. Device according to claim 11 or 12,characterized in that the central elements of the cage develop helicallyabout the axis.
 14. Device according to one of the claims 3 to 13,characterized in that the cage (40) is linked to the hub (50) by adisengageable driving mechanism (51,55,56,57) enabling free rotation ofthe cage.
 15. Device according to claim 14, characterized in that themechanism comprises means of disengagement in rotation under the effectof a borderline axial torque between the cage and the hub.
 16. Deviceaccording to claim 14 or 15, characterized in that the mechanismcomprises means of disengagement or disconnection in translation underthe effect of a borderline axial force between the cage and the hub. 17.Device according to one of the claims 1 to 16, characterized in that itcomprises a water tank positioned so as to bathe one part of the cage.18. Device according to one of the claims 1 to 17, characterized in thatit is designed to work with the axis (H-H) of the rotary cage (40)positioned in a horizontal direction.
 19. Device according to one of theclaims 1 to 18, characterized in that the lamp (10), with which it isdesigned to be used, is a medium-pressure mercury vapor lamp.
 20. Methodto test the ageing of samples characterized in that it implements aradiation exposure device according to any of the claims 1 to
 19. 21.Method according to claim 20, characterized in that it comprises thesteps consisting in: placing the samples in a sample-holder cage (40)that rotates about a horizontal axis (H-H), fixedly positioning andsupplying at least one electromagnetic radiation lamp (10) positioned onor about the axis (H-H) of horizontal rotation, generating a swirlingair flow about the horizontal rotation axis (H-H) the swirling air flowhaving, at the periphery of the cage, a rotational motion whosecomponent is included between the tangential direction and the radialdirection, the swirling air flow having a translation motion at thecenter of the cage, the component of which is substantially parallel tothe axial direction.